I used to worry about gifting a soap to a friend or family member that went bad, because it seems as if all oils have a specific shelf life (except jojoba - which is a wax). And if I understand correctly it is mostly the unsaponified oils that can go bad. I think the ones that combine with the lye are not as likely??? So it might also depend on how superfatted your soap is. I have very little soap left sitting around, but I do have a few friends that like to put out the soap I give them 'just for looks'. I do tell them that if they do not use them I will not gift them any more

. Since I am not selling I figure if a bar goes bad because they decided not to use it - well that is their own fault. One day I am going to write up a note to go with each soap.
So to answer your question: if selling I would keep my oils very simple - went to the farmers market today and it seems this is what most people do. Use oils that have a long shelf life. If just for yourself and family then use oil as fresh as possible. You could also put a use by date on the bar of soap.